A novel Stim1-dependent, non-capacitative Ca2+ entry pathway is activated by B cell receptor stimulation and depletion of Ca2+ stores

Abstract

In most non-excitable cells, the depletion of intracellular Ca(2+) stores activates capacitative Ca(2+) entry (CCE), which is a Ca(2+)-selective and La(3+)-sensitive entry pathway. Here, we report a novel mechanism of La(3+)-resistant Ca(2+) entry that is synergistically regulated by B cell receptor (BCR) stimulation and Ca(2+) store depletion (B-SOC). In the wild-type (WT) DT40 cells, BCR stimulation with anti-IgM antibodies induced Ca(2+) release and subsequent Ca(2+) entry in the presence of 0.3 microM La(3+) which blocks CCE completely. In the inositol 1,4,5-trisphosphate receptor-deficient (IP(3)R-KO) cells, BCR stimulation elicited neither Ca(2+) release nor Ca(2+) entry. However, under pretreatment of thapsigargin (ThG), BCR stimulation induced La(3+)-resistant Ca(2+) entry into both WT and IP(3)R-KO cells. These results indicate that BCR stimulation and Ca(2+) store depletion work in concert to activate the La(3+)-resistant Ca(2+) entry pathway. B-SOC was inhibited by tyrosine kinase inhibitor, genistein. In addition, B-SOC was completely abolished in Stim1-deficient cells and was restored by overexpression of yellow fluorescent protein (YFP)-tagged Stim1, but was unaffected by double knockdown of Orai1/Orai2. These results demonstrate a unique non-CCE pathway, in which Ca(2+) entry depends on Stim1 and tyrosine kinase activation. It is likely that similar regulation of Ca(2+) entry occurs in other cell types including salivary gland cells.